a) Field of the Invention
The present invention relates to a cylinder injection spark-ignition engine and relates specifically to a technique of quickening an activation of catalysts (catalytic converter) installed in an exhaust passage of the engine.
b) Description of the Related Art
When a temperature of the catalysts is low during an engine start under a cold ambient condition (so-called, a cold start) or when a poisoning of sulfur on catalysts or a smoke covering on the catalysts are advanced, it is demanded that the temperature of the catalysts be positively increased.
A Japanese Patent Application First Publication No. Heisei 8-296485 published on Nov. 12, 1996 exemplifies a previously proposed cylinder injection spark-ignition engine.
In the previously proposed cylinder injection engine, if the catalysts (catalytic converter or catalytic converter array) are needed to be heated, a main fuel is injected from each fuel injector at either a suction stroke or a compression stroke of each corresponding cylinder and an additional fuel is injected at the subsequent exhaust stroke thereof. In this case, an injection quantity of an additional fuel is controlled in such a manner that oxygen which is extra after the combustion of the main fuel is completely combusted.
In the above-identified Japanese Patent Application Publication, in a case where a rise in temperature of the catalysts is demanded to be more quickened, a fuel whose quantity is large to some degree and is based on a multiplication of a quantity by which the extra oxygen is completely combusted with a correction coefficient is injected as the additional fuel.
In order to increase the temperature of the catalysts as quick as possible with a supply of the additional fuel, it is effective to combust a large quantity of fuel within the exhaust passage by increasing a supply quantity of the additional quantity of the additional fuel. Specifically, in a case where the earlier activation of the catalysts is intended to be carried out midway through a warm-up of the engine, it is not only necessary to merely increase the temperature of the catalysts but also necessary to control an air-fuel mixture ratio appropriately.
For example, it is known that a temperature of the catalysts at which a purification reaction on the catalysts is started is shifted toward a lower temperature direction when the air-fuel mixture ratio is leaner to some degree with respect to the stoichiometric air-fuel mixture ratio.
However, in the previously proposed cylinder injection spark-ignition engine, a total air-fuel mixture ratio at a time when the temperature rise in the catalysts is controlled toward the air-fuel mixture ratio corresponding to the stoichiometric air-fuel mixture ratio or a richer ratio than the stoichiometric air-fuel mixture ratio.
Hence, there is a possibility that an efficient activation of the catalysts cannot always be achieved if the above-described control technique is applied to the earlier activation of the catalysts.
It is therefore an object of the present invention to provide improved cylinder injection spark-ignition engine and method applicable to the cylinder injection spark-ignition engine which can achieve an efficient activation of the catalysts.
The above-described object can be achieved by providing a cylinder injection spark-ignition engine, comprising: a spark plug to ignite an air mixture fuel in a combustion chamber; a fuel injector to inject fuel directly into the combustion chamber; a catalytic converter interposed in an exhaust passage; and a controller, programmed to: command the fuel injector to inject a main fuel into the combustion chamber for a first time duration within at least one of a suction stroke and a compression stroke and to inject additional fuel for a second time duration within at least one of an expansion stroke and an exhaust stroke; to set a target total air-fuel mixture ratio for a warm-up condition of the catalytic converter, the target total air-fuel mixture ratio being leaner than a stoichiometric air-fuel mixture ratio; and to calculate a fuel injection quantity Ti1 of the main fuel and a fuel injection quantity Ti2 of the additional fuel in such a manner that the total air-fuel mixture ratio based on a sum of the main fuel and the additional fuel corresponds to the target total air-fuel mixture ratio.
The above-described object can also be achieved by providing a method applicable to a cylinder injection spark-ignition engine, the cylinder injection spark ignition engine including: a spark plug to ignite an air mixture fuel in a combustion chamber; a fuel injector to inject fuel into a combustion chamber; and a catalytic converter interposed in an exhaust passage, the method comprising: setting a target value of a total air-fuel mixture ratio to a value of the air-fuel mixture ratio which is leaner than a stoichiometric air-fuel mixture ratio for a warm-up condition of the catalytic converter; calculating respective injection quantities Ti1 and Ti2 of the main fuel and the additional fuel in such a manner that the total air-fuel mixture ratio based on a sum of the main fuel and the additional fuel corresponds to the set target value of the total air-fuel mixture ratio; and commanding the fuel injector to inject a main fuel into the combustion chamber for a first time duration within at least one of a suction stroke and a compression stroke and to inject an additional fuel for a second time duration within at least one of an expansion stroke and an exhaust stroke.